WLAN's of various kinds are known in the art including, but not limited to, 802.11 compatible systems (such as 802.11(a), 802.11(b), 802.11(g) and so forth). Such systems allow a portable computing device to be used at various locations within the coverage area of the WVLAN in a fairly transparent manner with respect to the user's perception regarding connectivity. For example, although a given WLAN may be comprised of a plurality of access points (AP's), the user will often have no particular sense of which AP is presently supporting their mobile unit's communications needs.
Such WLAN's are capable of supporting a wide variety of communication needs including but not limited to voice communications (such as so-called Voice-over-Internet-Protocol (VoIP) communication services). When available, such voice services can be very desirable as often such services, including even long distance telephony, can be accomplished with essentially little or no incremental additional cost to the user. Notwithstanding such benefits, however, there are some impediments to widespread application and use of such services. For example, the user must have a handset (or other platform) that will support such services. This requirement can be troubling to some users who wish to only have and utilize a single communication platform. Such users will typically eschew use of a separate device that offers the benefits of WLAN connectivity in favor of a single wide area network (WAN) device such as a cellular telephone that will offer essentially ubiquitous coverage.
To meet the requirements of such users, it has been proposed that a single portable device can be configured as both a WAN device and a WLAN device such that a single device can support and facilitate voice communications (or other desired communications) in both a WAN operating environment and in a WLAN operating environment when available. Unfortunately, a simplistic combination of two such capabilities in a single housing, while quite attainable, does not address all of the user's needs. As one important example, without further integration between such operability, the user can experience a dropped communication when they begin a communication using the WLAN capability of the device but, during the course of that communication, leave the coverage area of the WLAN.
One proposed solution is to facilitate a handoff of the on-going communication from the WLAN to the WAN during the course of such a communication. While such a capability would appear to address this particular need, implementation of such a capability poses numerous challenges. In particular, present system dynamics mitigate strongly in many operating scenarios against being able to actually effect a handoff during the course of the communication. For example, while it can consume many seconds (such as more than ten seconds) to complete the entire process of acquiring a WAN link and switching the WLAN communication over to the WAN link, the user can leave the effective coverage area of the WLAN in considerably less time. As a result, the time that intervenes between when the device or system can ascertain that a handoff is required and when the device is unsupported by the WLAN is often considerably less than what is required to ensure a handoff of a presently on-going communication. Instead, the WLAN link will be lost and dropped prior to when the WAN link can be brought up and rendered able to accept the WLAN-supported communication.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are typically not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention.